Psalms 90:10 indicates a generation as three score and ten - i.e. 70 years. btw, King David died at 70 years old.
But this has nothing to do with Matt 24:32. The Greek word Genea also has been translated as an "age," which is defined as a long period of time and is equivalent to the time-period for a "Day of the Lord" and in 2 Peter 3:8 and Ps 90:4 we are told that a Day of the Lord is like a 1,000-years for mankind.
You are wrongly forcing an understanding of a "descendant generation" upon the Greek word "Genea"
below is a list of verses when the Greek Root Word is embedded within 9 Greek words:-
Now looking at the first 4 reference to Genea they do not speak of a descendant generation as you are suggesting but rather they are referring to an indeterminate time period or age/generation where the people that Jesus was speaking to were either adulterous or perverse and that this characteristic was common to a number of descendant generations such that to be consistent Mar 24:34 is not referring to a descendant generation as you are insisting on in your understanding.
Matt 12:39: - 39 He answered, "A wicked and adulterous
generation asks for a miraculous sign! But none will be given it except the sign of the prophet Jonah.
Matt 16:4: - 4 A wicked and adulterous
generation seeks after a sign, and no sign shall be given to it except the sign of the prophet Jonah." And He left them and departed.
Matt 17:17: - 17 Then Jesus answered and said, "O faithless and perverse
generation, how long shall I be with you? How long shall I bear with you? Bring him here to Me."
Matt 24:34: - 34 Assuredly, I say to you, this
generation will by no means pass away till all these things take place.
Goodbye